<?php
class MY_Form_validation extends CI_Form_validation { 
        public function is_unique($str, $field) 
        { 
            if (substr_count($field, '.')==3) 
            { 
                list($table,$field,$id_field,$id_val) = explode('.', $field); 
                $query = $this->CI->db->limit(1)->where($field,$str)->where($id_field.' != ',$id_val)->get($table);    
            } 
            else 
            { list($table, $field)=explode('.', $field); 
                $query = $this->CI->db->limit(1)->get_where($table, array($field => $str)); 
                
            } 
                return $query->num_rows() === 0; 
                
        }
     
} 
  